A powder bed fusion apparatus, as illustrated in FIG. 13, is equipped with a laser beam outputting section (energy beam emitting section) 201, a thin layer forming section 202 where a thin layer of a powder material is formed and then the layer is fused by a laser beam (energy beam) to perform modeling, a recoater 60 which moves on a surface of the thin layer forming section 202 and carries the powder material, and a control section 203 which controls modeling.
Further, the thin layer forming section 202, as illustrated in FIG. 14, is equipped with powder material housing containers 52a, 52b which house a powder material 59, and a thin layer forming container 51 in which a thin layer 59a of the powder material is formed. Furthermore, the thin layer forming container 51 has a built-in heater, and heaters 54a, 54b or an infrared lamp are also arranged around the thin layer forming container 51.
By using the powder bed fusion apparatus, as illustrated in FIGS. 15A to 15C, the powder material 59 from the powder material housing container 52a is carried into the thin layer forming container 51 to form the thin layer 59a of the powder material on a part table 55, and furthermore, a residual powder material is housed into the powder material housing container 52b. 
Next, as illustrated in FIGS. 15D to 15F, a certain region of the thin layer 59a is heated by a laser beam 61, and the region is melted and solidified to form a subsequently solidified layer 59b as the first layer.
Subsequently, the recoater 60 is moved to the left according to the above-described action to form a subsequently solidified layer 59b as the second layer and so on.
After that, the above-described actions are repeated. Thus, the subsequently solidified layers 59b and the like are stacked for several hundred layers or several thousand layers to fabricate a three-dimensional model.
Herein, the thin layer 59a of the powder material formed in the thin layer forming container 51 is preliminarily heated to temperature near melting temperature of the powder material 59 by the heater or the like before irradiation of the laser beam 61.
Patent Documents (Japanese Patent Laid-open No. 2008-155538, No. 2010-173123 etc.) describe such a powder bed fusion method.
However, immediately after the thin layer 59a of the powder material is formed, temperature of a peripheral region of the thin layer 59a generally tends to be lower than that of a central region, and thus uniformity of temperature in the entire thin layer 59a is not maintained. When the laser beam 61 is irradiated in such a state, a temperature difference between a melted area and its surrounding area becomes larger, which causes generation of warp.
Therefore, as illustrated in FIG. 15D, irradiation of the laser beam 61 is performed after a temperature is stabilized at a set temperature and becomes even on the entire thin layer 59a of the powder material in the thin layer forming container 51.
However, even after housing the residual powder material 59 into the powder material housing container 52b, about a few seconds of waiting time is still necessary per one subsequently solidified layer. For this reason, time loss becomes very large when several thousand subsequently solidified layers are stacked.